Asthma is a disease effecting approximately 20 million Americans. The death rates from asthma have increased substantially since 1979, increasing for children over five years of age from the period from 1979 to 1982. Hospitalization rates for asthma increased by 50% for adults in that period and by over 200% for the period from 1965 to 1983. Hospitalization rates for black patients are 50% higher for adults and 150% higher for children than the general population. (R. Evans et al., "National Trends in the Morbidity and Mortality of Asthma in the U.S.," Chest (1987) 91(6) Sup., 65S-74S). Increasing asthma mortality rates for the same period of time has been documented in other countries. (R. Jackson et al., "International Trends in Asthma Mortality: 1970-1985," Chest (1988) 94, 914-19.)
The mainstay for the management of asthma as well as other respiratory diseases in the United States has been inhaled aerosolized medication. The primary aerosolized drugs currently prescribed for respiratory therapy in the United States are anti-inflammatory drugs, bronchodilators and enzymes. These medications can be self-administered by patients using hand held metered dose inhalers (MDIs). Bronchodilators, while useful for the management of an acute asthma attack, are currently not the preferred drugs of choice for long-term asthma management. Aerosolized anti-inflammatory drugs, such as inhaled steroids and cromoglycates, used in conjunction with objective measures of therapeutic outcome are the preferred tools for long-term management of the asthmatic patient. (U.S. Department of Health and Human Services, "Guidelines for the Diagnosis and Management of Asthma," National Asthma Education Program Expert Panel Report, pub. no. 91-3042, August 1991.)
A rational program for self-administration of aerosolized asthma therapeutic drugs would include: a) avoidance of overuse of bronchodilators, given that all bronchodilator drugs may be potentially toxic when used in excess (W. Spitter et al., "The Use of B-Agonists and the Risk of Death and Near Death from Asthma," N. Engl J. Med (1992) 326, 501-6); and b) using an anti-inflammatory drug on a prescribed scale which may include regular dosing several times a day (J. L. Malo et al., "Four-times-a-day Dosing Frequency Is Better than Twice-a-day Regimen in Subjects Requiring a High-dose Inhaled Steroid, Budesonide, to Control Moderate to Severe Asthma," Am Rev Respir Dis (1989) 140, 624-28).
Existing metered dose inhaler devices deliver aerosolized medication to areas which are not specifically targeted. For example, some devices can deliver aerosolized medication to the outermost areas of the lung (peripheral region where gases are exchanged) here the drug would be absorbed into the circulatory system and have a systemic effect as opposed to a topical effect on bronchial airways (the intermediate region) which have an approximate diameter of 1 mm. Other devices deliver a large fraction of the aerosolized dose to the oropharynx and larger airways. When certain drugs such as steroids are delivered to the back of the throat the effects can be adverse such as candida which results from the delivery of corticosteroids to the back of the throat. Thus, it can be seen that it is important that topically effective medications be efficiently delivered to the desired region of the lung and that they not be delivered to other areas. The present invention endeavors to provide a device and method for achieving such.